Local interconnect having increased misalignment tolerance

ABSTRACT

A method is provided for forming an interconnect in a semiconductor memory device. The method includes forming a pair of source select transistors on a substrate. A source region is formed in the substrate between the pair of source select transistors. A first inter-layer dielectric is formed between the pair of source select transistors. A mask layer is deposited over the pair of source select transistors and the inter-layer dielectric, where the mask layer defines a local interconnect area between the pair of source select transistors having a width less than a distance between the pair of source select transistors. The semiconductor memory device is etched to remove a portion of the first inter-layer dielectric in the local interconnect area, thereby exposing the source region. A metal contact is formed in the local interconnect area.

TECHNICAL FIELD

Implementations consistent with the principles of the invention relategenerally to semiconductor devices and methods of manufacturingsemiconductor devices. The invention has particular applicability tonon-volatile memory devices.

BACKGROUND ART

The escalating demands for high density and performance associated withnon-volatile memory devices require small design features, highreliability and increased manufacturing throughput. The reduction ofdesign features, however, challenges the limitations of conventionalmethodology. For example, the reduction of design features makes itdifficult for the memory device to meet its expected data retentionrequirement.

One type of conventional electrically erasable programmable read onlymemory (EEPROM) device includes a silicon substrate with anoxide-nitride-oxide (ONO) stack formed on the substrate. A siliconcontrol gate is formed over the ONO stack. This type of memory device isoften referred to as a SONOS (silicon-oxide-nitride-oxide-silicon) typememory device. In a SONOS device, the nitride layer acts as the chargestorage layer. In an alternative EEPROM design, the charge storage layermay include a polysilicon floating gate. In a more specificimplementation, EEPROM memory devices of these types may be implementedas an array of memory cells configured in a NAND arrangement.

DISCLOSURE OF THE INVENTION

In an implementation consistent with the principles of the invention, amethod is provided for forming an interconnect in a semiconductor memorydevice. The method includes forming a pair of source select transistorson a substrate. A source region is formed in the substrate between thepair of source select transistors. A first inter-layer dielectric isformed between the pair of source select transistors. A mask layer isdeposited over the pair of source select transistors and the firstinter-layer dielectric, where the mask layer defines a localinterconnect area between the pair of source select transistors having awidth less than a distance between the pair of source selecttransistors. The semiconductor memory device is etched to remove aportion of the first inter-layer dielectric in the local interconnectarea, thereby exposing the source region. A metal contact is formed inthe local interconnect area.

In another implementation consistent with the principles of theinvention, a semiconductor device is provided. The semiconductor deviceincludes a substrate having a source region formed in an active region.A pair of source select transistors is formed above the substrate onopposite sides of the source region. A first inter-layer dielectric isformed above the substrate in between the pair of source selecttransistors. A local interconnect comprising a metal is formed adjacentthe first inter-layer dielectric, where the local interconnect has awidth narrower than a distance between the pair of source selecttransistors.

In yet another implementation consistent with the principles of theinvention, a method of fabricating a semiconductor device having a pairof select transistors formed over a substrate is provided. The methodincludes: forming a source region between the pair of selecttransistors, the source region have a silicide region formed in an uppersurface thereof, forming a liner oxide layer over the pair of selecttransistors and the source region; forming spacers adjacent the interiorsidewalls of the pair of select transistors over the liner oxide layer;depositing a inter-layer dielectric between the spacers; etching theinter-layer dielectric and the liner oxide layer to form a localinterconnect area have a width less than a distance between the pair ofselect transistors; and forming a metal contact within the localinterconnect area.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate an embodiment of the inventionand, together with the description, explain the invention. In thedrawings,

FIG. 1 illustrates an exemplary configuration of a semiconductor devicein an implementation consistent with the principles of the invention;

FIGS. 2A-2B illustrate an exemplary process for forming a semiconductormemory device in an implementation consistent with the principles of theinvention; and

FIGS. 3-9 illustrate exemplary views of a semiconductor memory devicefabricated according to the processing described in FIGS. 2A-2B.

BEST MODE FOR CARRYING OUT THE INVENTION

The following detailed description of implementations consistent withthe principles of the invention refers to the accompanying drawings. Thesame reference numbers in different drawings may identify the same orsimilar elements. Also, the following detailed description does notlimit the invention. Instead, the scope of the invention is defined bythe appended claims and their equivalents.

FIG. 1 illustrates an exemplary configuration of a semiconductor device100, such as a flash EEPROM semiconductor device. Semiconductor device100 may include a plurality of memory cells 102 arranged in arectangular matrix or array of rows and columns and include a pluralityof bit lines (BL) associated with each column, a plurality of word lines(WL) 104 associated with each row and a plurality of select lines (SL)coupled to select source transistors 106.

As illustrated, semiconductor device 100 may include rows of memorycells 102 along word lines 104 formed in the active regions ofsemiconductor device 100. Semiconductor device 100 may also include rowsof select source transistors 106 in the active regions. Semiconductordevice 100 may also include a source line 108 (shown as via the dottedlines in FIG. 1) as is known in the art. In one implementation, eachcell 102 includes a source and drain formed in a semiconductorsubstrate, a tunnel oxide layer, a charge storage layer, and a controlgate separated from the charge storage layer by an inter-gatedielectric.

Additional details regarding the formation of device 100 will bedescribed below in relation to FIGS. 2-9. As can be appreciated, thecells 102 of memory device 100 differ from conventional FETs in thatthey include the charge storage layer and tunnel oxide layer disposedbetween the control gate and the semiconductor substrate in which thesource and drain are formed.

EXEMPLARY PROCESSING

FIGS. 2A-2B illustrates an exemplary process for forming a semiconductormemory device in an implementation consistent with the principles of theinvention. In one implementation, the semiconductor memory deviceincludes an array of memory cells and transistors in a flash memorydevice, such as that illustrated in FIG. 1. FIGS. 3-9 illustrateexemplary views of a semiconductor memory device taken along line X-X′in FIG. 1 fabricated in accordance with principles of the invention.

With reference to FIGS. 2A and 3, processing may begin with asemiconductor device 300 having a defined structure. As shown in FIG. 3,semiconductor device 300 may initially include a substrate layer 310having a source region 312 and merged source/drain regions 314 formedtherein, a number of memory cells 316 formed over the substrate layer310, gate silicide regions 318 formed in memory cells 316, a sourcesilicide region 320 formed in source region 312, a first dielectriclayer 322 formed over the substrate 310 and memory cells 316, and asecond dielectric layer 324 (e.g., spacers) formed over the firstdielectric layer 322. Only two memory cells 316, two source selecttransistors 334, one source region 312, and four merged source/drainregions 314 are shown in FIG. 3 for simplicity. It should be understoodthat semiconductor device 300 may include a larger number of memorycells 316, source select transistors 334, source regions 312 and mergedsource/drain regions 314.

In an exemplary embodiment, layer 310 may be a crystalline substrate ofsemiconductor device 300 and may include silicon, germanium,silicon-germanium or other semiconducting materials. In alternativeimplementations, layer 310 may be a conductive layer formed a number oflayers above the surface of a substrate in semiconductor device 300. Asis known in the art, substrate layer 310 may include conventionalfeatures, such as P-well implants, etc., the descriptions of which arenot provided herein to not unduly obscure the thrust of the presentinvention.

Memory cells 316 may be formed in a conventional manner, as illustratedin FIG. 3 (act 200). In one implementation consistent with principles ofthe invention, memory cells 316 may include SONOS-type memory cells,where each memory cell 316 includes a tunnel oxide layer 326, a nitridecharge storage layer 328, an inter-gate dielectric layer 330, and apolysilicon control gate layer 332. In alternative implementations,memory cells 316 may be floating gate memory cells, with each cellhaving a silicon control gate electrode 332, an ONO layer 330, apolysilicon floating gate electrode 328 and a tunnel oxide layer 326formed on substrate 310. In an even more specific implementation, chargestorage layer 328 may act as a multi-bit or dual bit charge storagelayer for storing multiple bits in each memory cell 316.

Source select transistor 334 may define a source line interconnect area336 for semiconductor device 300. A distance between source selecttransistors 334 may range from about 1500 Å to about 10,000 Å.Additional details regarding subsequent formation of source lineinterconnect will be set forth in additional detail below.

Source region 312 and merged source/drain regions 314 may be formed insubstrate 310 in a conventional manner (act 202). For example, n-type orp-type impurities may be implanted in substrate 310 to form theseregions. The particular implantation dosages and energy used to formsource region 312 and merged source/drain regions 314 may be selectedbased on the particular end device requirements. One of ordinary skillin the art would be able to optimize the source/drain implantationprocess based on the particular circuit requirements. It should also beunderstood that source region 312 and merged source/drain regions 314may alternatively be formed at other points in the fabrication processof semiconductor device 300. For example, sidewall spacers (e.g., seconddielectric layer 324) may be formed prior to the source/drain ionimplantation to control the location of the source/drain junctions basedon the particular circuit requirements.

Gate silicide regions 318 may be formed in polysilicon control gatelayer 332 of memory cells 316 in a conventional manner (act 204). In oneimplementation consistent with principles of the invention, a metal,such as tungsten, cobalt, titanium, tantalum or molybdenum, may bedeposited on the upper surfaces of polysilicon control gates 332 to athickness ranging from about 50 Å to about 500 Å. A thermal annealingmay then be performed to create a metal-silicide structure 318. In oneimplementation, the thermal anneal is performed at a temperature rangingfrom about 300° C. to about 1000° C.

Source silicide region 320 may be formed on at least a portion of thetop surface of source region 312, as illustrated in FIG. 1 (act 206).For example, a metal, such as tungsten, cobalt, titanium, tantalumnickel or molybdenum, may be deposited on the upper surfaces of sourceregion 312 to a thickness ranging from about 50 Å to about 500 Å. Athermal annealing may then be performed to create a metal-silicidestructure 320. In one implementation, the thermal anneal is performed ata temperature ranging from about 300° C. to about 1000° C.

First dielectric layer 322 may be formed over substrate layer 310 andmemory cells 316 in a conventional manner (act 208). In oneimplementation consistent with principles of the invention, firstdielectric layer 322 may include a dielectric material, such as silicondioxide (SiO₂) and may function as a liner oxide in semiconductor device300. In one exemplary embodiment, first dielectric layer 322 may be asilicon dioxide layer having a thickness ranging from about 50 Å toabout 500 Å. In one implementation consistent with principles of theinvention, the distance between respective interior surfaces of firstdielectric layer 322 on interior sidewalls of source select transistors334, rather than the distance between cells 334 is defined as D1.

Second dielectric layer 324 may be formed in a conventional manner overfirst dielectric layer 322, as shown in FIG. 1 (act 210). Seconddielectric layer may be formed of a dielectric material, such as siliconnitride or “nitride” (e.g., Si₃N₄) and may function as a spacer layer insemiconductor device 300. In one implementation, second dielectric layer324 is deposited on semiconductor device 300 by low pressure chemicalvapor position (LPCVD). The deposited layer 324 may then beanisotropically etched to form final spacer layer 324.

Following spacer formation, a dielectric etch stop layer 410 may beformed in a conventional manner over semiconductor device 300, asillustrated in FIG. 4 (act 212). In one implementation consistent withprinciples of the invention, dielectric etch stop layer 410 may includea dielectric material, such as a silicon nitride (e.g., Si₃N₄) orsilicon oxynitride (SiON) and may function as an etch stop layer duringsubsequent processing of semiconductor device 300. In one exemplaryembodiment, dielectric etch stop layer 410 is a silicon nitride layerhaving a thickness ranging from about 100 Å to about 1000 Å.

A first inter-layer dielectric layer (referred to herein as “ILD0”) 510may be deposited over semiconductor device 300 in a conventional mannerto fill the space between all devices fabricated on substrate 310 (act214). In one implementation consistent with principles of the invention,ILD0 510 may include a dielectric material, such as silicon dioxide(SiO₂). ILD0 510 may then be selectively polished back using, e.g., aselective slurry such as a ceria-based slurry to expose an upper surfaceof etch stop layer 410, as illustrated in FIG. 5 (act 216). It should beunderstood that any suitable chemical-mechanical polishing (CMP)techniques may be used to polish ILD0 510.

Following polishing of ILD0 510, a mask layer 610 may be patterned andformed over semiconductor device 300, as shown in FIG. 6 (act 218). Masklayer 610 may be conventionally formed by patterning a photoresist layerusing ultraviolet light to define areas to be protected duringsubsequent etching steps. In the current implementation, mask layer 610is patterned to define a local interconnect opening 620 formed abovesource region 312 in substrate layer 310.

Consistent with principles of the invention, mask layer 610 may bespecifically patterned to define a local interconnect opening 620 havinga width D2 that is slightly smaller than the width D1, between interiorsurfaces of first dielectric layer 322 on the interior sidewalls ofsource select cells 334, as described above. In one implementationconsistent with principles of the invention, D2 is approximately 40 to60 nm less than the width D1. More specifically, each interior edge ofmask layer 610 may be approximately 20 to 30 nm offset from thecorresponding interior edge of first dielectric layer 322, in order toprovide a suitable misalignment budget for ensuring that a subsequentlyformed interconnect will be formed between source select transistors 334while simultaneously providing fully access to source silicide region320 in substrate 310.

Following formation of mask layer 610, semiconductor device 300 may beetched to remove ILD0 510, stop layer 410, and first dielectric layer322 in the region defined by mask layer 610 and nitride spacers 324,thereby forming local interconnect opening 710, as illustrated in FIG. 7(act 220). In one implementation consistent with principles of theinvention, semiconductor device 300 may be etched using a dry plasmaetch that first selectively removes ILD0 510 without removing stop layer410. The etch chemistry may then be changed to facilitate removal ofdielectric etch stop layer 410 and liner oxide layer 322, withoutremoving spacers 324 (act 221). As shown in FIG. 7, by maximizing thewidth of local interconnect opening 710 (D2) to the limits allowed bythe misalignment budget, full contact of a subsequently formed contactmaterial with the source silicide region 320 may be achieved. Mask layer610 may then be removed in a conventional manner (act 222).

A barrier metal layer 810 may then be deposited within localinterconnect opening 710 in a conventional manner, as illustrated inFIG. 8 (act 224). In one exemplary implementation, barrier metal layer810 may be a titanium (Ti) followed by a titanium nitride (TiN) layerhaving a having a thickness ranging from about 50 Å to about 300 Å forboth materials. Following deposition of barrier metal layer 810, a metalcontact layer 820 may be deposited within interconnect 710 opening, asillustrated in FIG. 8 (act 226). In one exemplary implementation, metalcontact layer 820 may be formed of tungsten, copper, or aluminum havinga thickness ranging from about 1000 Å to about 10,000 Å.

Barrier metal layer 810 and metal contact layer 820 may be planarized toform a metal strap (e.g., a tungsten strap), as illustrated in FIG. 8(act 228). In one implementation consistent with principles of theinvention, layers 810 and 820 may be planarized using a conventional CMPprocess.

A second inter-layer dielectric layer (referred to herein as “ILD0.5”)910 may then be formed over semiconductor device 300, as illustrated inFIG. 9 (act 230). In one implementation consistent with principles ofthe invention, ILD0.5 may be an oxide material (e.g., SiO₂) having athickness ranging from about ranging from about 1000 Å to about 10,000Å. ILD0.5 910 may then be planarized using, e.g., a CMP process tofacilitate formation of subsequent structures, such as interconnectlines (act 232). It should be understood that any suitable planarizingtechniques may be used to planarize ILD0.5 910.

Following planarizing of ILD0.5 910, a mask layer (not shown) may bepatterned and formed over semiconductor device 300, to define a contactregion in ILD0.5 910 (act 234). ILD0.5 910 may then be etched to removeILD0.5 910 in the region defined by the mask layer, thereby forming asource contact hole 920, as illustrated in FIG. 9 (act 236). In oneimplementation consistent with principles of the invention, ILD0.5 910may be etched using a dry plasma etch that selectively removes ILD0.5910. The mask layer may then be removed following completing of theetching of act 236 (act 238).

A second barrier metal layer 930 may then be deposited within sourcecontact hole 920 in a conventional manner, as illustrated in FIG. 9 (act240). In one exemplary implementation, second barrier metal layer 930may be a titanium (Ti) followed by a titanium nitride (TiN) layer, eachhaving a having a thickness ranging from about 50 Å to about 300 Å.Following deposition of second barrier metal layer 930, a second metalcontact layer 940 may be deposited within source contact hole 920 (act242). In one exemplary implementation, second metal contact layer 940may be formed of tungsten, copper or aluminum and may have a thicknessranging from about 1000 Å to about 10,000 Å. Second barrier metal layer930 and second metal contact layer 940 may be polished back to form ametallized contact. A metal interconnect (M1) 950 (e.g., tungsten,copper or aluminum) may then be formed on an upper surface of theplanarized metal contact layer 940 in a conventional manner to establishan electrical connection to the metallized source line (act 246).

Additional ILDs and metal lines may be formed to complete thefabrication of semiconductor device 300 based on the particular circuitrequirement. For example, additional ILD's and metal layers may beformed over metal interconnect 950. A top dielectric layer, alsoreferred to as cap layer, may also be formed over a top most conductiveline. The cap layer may act as a protective layer to prevent damage toconductive lines and other portions of semiconductor device 300 duringsubsequent processing. For example, cap layer may protect semiconductordevice 300 against impurity contamination during subsequent cleaningprocesses that may be used to complete a working memory device.

CONCLUSION

The foregoing description of exemplary embodiments of the inventionprovides illustration and description, but is not intended to beexhaustive or to limit the invention to the precise form disclosed.Modifications and variations are possible in light of the aboveteachings or may be acquired from practice of the invention. Forexample, in the above descriptions, numerous specific details are setforth, such as specific materials, structures, chemicals, processes,etc., in order to provide a thorough understanding of the invention.However, implementations consistent with the invention can be practicedwithout resorting to the details specifically set forth herein. In otherinstances, well known processing structures have not been described indetail, in order not to unnecessarily obscure the thrust of the presentinvention. In practicing the invention, conventional deposition,photolithographic and etching techniques may be employed, and hence, thedetails of such techniques have not been set forth herein in detail.

While a series of acts has been described with regard to FIGS. 2A-2B,the order of the acts may be varied in other implementations consistentwith the invention. Moreover, non-dependent acts may be implemented inparallel.

No element, act, or instruction used in the description of the presentapplication should be construed as critical or essential to theinvention unless explicitly described as such. Also, as used herein, thearticle “a” is intended to include one or more items. Where only oneitem is intended, the term “one” or similar language is used. Further,the phrase “based on” is intended to mean “based, at least in part, on”unless explicitly stated otherwise.

1. A method for forming an interconnect in a semiconductor memorydevice, the method comprising: forming a pair of source selecttransistors on a substrate, where forming each of the pair of sourceselect transistors comprises: forming a first dielectric layer on thesubstrate, forming a charge storage layer on the first dielectric layer,forming a second dielectric layer on the charge storage layer, andforming a control gate layer on the second dielectric layer; forming asource region in the substrate between the pair of source selecttransistors; forming a first inter-layer dielectric between the pair ofsource select transistors; depositing a mask layer over the pair ofsource select transistors and the first inter-layer dielectric, wherethe mask layer defines a local interconnect area between the pair ofsource select transistors having a width less than a distance betweenthe pair of source select transistors; etching the semiconductor memorydevice to remove a portion of the first inter-layer dielectric in thelocal interconnect area, thereby exposing the source region; and forminga metal contact in the local interconnect area.
 2. The method of claim1, where the width of the local interconnect area is between 40 nm and60 nm less than a distance between the pair of source selecttransistors.
 3. The method of claim 1, where the control gate layer is apolysilicon layer having a thickness ranging from about 1000 Å to about2000 Å.
 4. The method of claim 1, where the charge storage layer is asilicon nitride layer having a thickness ranging from about 25 Å toabout 500 Å.
 5. The method of claim 4, where the silicon nitride layeris configured to store more than one bit of information therein.
 6. Themethod of claim 1, further comprising: forming a gate silicide region inthe control gate layer of each source select transistors.
 7. The methodof claim 1, further comprising: forming a source silicide region in thesource region.
 8. The method of claim 1, further comprising, prior toforming the first inter-layer dielectric: forming a dielectric linerlayer over the substrate and the pair of source select transistors; andforming a spacer layer over the dielectric liner layer, where the spacerlayer is etched to expose at least a portion of the dielectric linerlayer over the source region.
 9. The method of claim 8, furthercomprising forming a dielectric etch stop layer over the spacer layerand the dielectric liner layer prior to forming the first inter-layerdielectric.
 10. The method of claim 9, where the dielectric etch stoplayer is a silicon nitride layer having a thickness ranging from about100 Å to about 1000 Å.
 11. The method of claim 9, further comprisingpolishing the first inter-layer dielectric to expose an upper surface ofthe dielectric etch stop layer.
 12. The method of claim 11, wherepolishing the first inter-layer dielectric is performed by subjectingthe semiconductor memory device to a selective slurry.
 13. The method ofclaim 9, where etching the semiconductor memory device, to remove aportion of the first inter-layer dielectric in the local interconnectarea, further comprises: etching the first inter-layer dielectric withinthe local interconnect area using a first etch chemistry; and etchingthe dielectric stop layer and dielectric liner layer using a second etchchemistry.
 14. A method of fabricating a semiconductor device having apair of select transistors formed over a substrate, the methodcomprising: forming a source region between the pair of selecttransistors, the source region have a silicide region formed in an uppersurface thereof; forming a liner oxide layer over the pair of selecttransistors and the source region; forming spacers adjacent the interiorsidewalls of the pair of select transistors over the liner oxide layer;depositing a inter-layer dielectric between the spacers; etching theinter-layer dielectric and the liner oxide layer to form an interconnectarea have a width less than a distance between the pair of selecttransistors; and forming a metal contact within the interconnect area.15. The method of claim 14, where the width of the interconnect area isbetween 40 and 60 nm less than a distance between the pair of sourceselect transistors.
 16. The method of claim 14, further comprisingforming at least one of the pair of source select transistors, theforming comprising: forming a first dielectric layer on the substrate,forming a charge storage layer on the first dielectric layer, forming asecond dielectric layer on the charge storage layer, and forming acontrol gate layer on the second dielectric layer.
 17. A methodcomprising: forming a pair of source select transistors on a substrateof a semiconductor memory device; forming a source region in thesubstrate between the pair of source select transistors; forming a firstinter-layer dielectric between the pair of source select transistors;depositing a mask layer over the pair of source select transistors andthe first inter-layer dielectric, where the mask layer defines a localinterconnect area between the pair of source select transistors having awidth less than a distance between the pair of source selecttransistors; etching the semiconductor memory device to remove a portionof the first inter-layer dielectric in the local interconnect area,thereby exposing the source region; forming a barrier metal layer in thelocal interconnect area prior to forming a metal contact; and formingthe metal contact in the local interconnect area.
 18. The method ofclaim 17, further comprising, prior to forming the first inter-layerdielectric: forming a dielectric liner layer over the substrate and thepair of source select transistors; and forming a spacer layer over thedielectric liner layer, where the spacer layer is etched to expose atleast a portion of the dielectric liner layer over the source region.19. The method of claim 18, further comprising forming a dielectric etchstop layer over the spacer layer and the dielectric liner layer prior toforming the first inter-layer dielectric.
 20. The method of claim 17,where the barrier metal layer is one of titanium layer followed by atitanium nitride layer, each layer having a thickness ranging from about50 Å to about 300 Å; and the metal contact comprises tungsten, where themetal contact is polished to form a tungsten strap.